Phép cộng phân số

số thóc dành cho đàn bồ câu 

1-1/4-2/3=1/12 

Coi số thóc là 1

Số thóc dành cho cả gà và vịt là:

1/4 + 2/3 = 3/12 + 8/12 = 11/12

Số thóc dành cho đàn bồ câu là:

1 - 11/12 = 12/12 - 11/12 = 1/12

Đáp số: 1/12

4/3

A = 1/3 + 2/3 + 1/3

A = 1 + 1/3

A = 4/3

1/3+2/3+1/3

=4/3

giúp mềnh ới

\(\Leftrightarrow\dfrac{-7}{x-3}=\dfrac{x-3}{-7}\)

\(\Leftrightarrow\left(x-3\right)^2=49\)

\(\Leftrightarrow\left[{}\begin{matrix}x-3=7\\x-3=-7\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=10\\x=-4\end{matrix}\right.\)

`(-7)/(x-3) = (3-x)/7`

`<=> (-7)/x-3)=(x-3)/-7`

`=> `(x-3)(x-3)=(-7).(-7)`

`=>` \(\left[{}\begin{matrix}\left(x-3\right)^2=-7^2\\\left(x-3\right)^2=7^2\end{matrix}\right.\)

`=>` \(\left[{}\begin{matrix}x-3=-7\\x-3=7\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x=-7+3\\x=7+3\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x=-4\\x=10\end{matrix}\right.\)

`(x-1/3)^2=25/9`

`(x-1/3)^2=(5/3)^2` hoặc `(x-1/3)^2=(-5/3)^2`

`@TH1: x-1/3=5/3=>x=5/3+1/3=6/3=2`

`@TH2: x-1/3=-5/3=>x=-5/3+1/3=-4/3`

`(x-1/3)^2 = 25/9`

`=>` \(\left[{}\begin{matrix}\left(x-\dfrac{1}{3}\right)^2=\left(\dfrac{5}{3}\right)^2\\\left(x-\dfrac{1}{3}\right)^2=\left(-\dfrac{5}{3}\right)^2\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x-\dfrac{1}{3}=\dfrac{5}{3}\\x-\dfrac{1}{3}=-\dfrac{5}{3}\end{matrix}\right.\)

`=>`\(\left[{}\begin{matrix}x=2\\x=-\dfrac{4}{3}\end{matrix}\right.\)

`(x-1/3)^2 = 25/9`

`(x-1/3)^2 = (+- 5/3)^2`

\(\Rightarrow\left[{}\begin{matrix}x-\dfrac{1}{3}=\dfrac{5}{3}\\x-\dfrac{1}{3}=-\dfrac{5}{3}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{5}{3}+\dfrac{1}{3}\\x=-\dfrac{5}{3}+\dfrac{1}{3}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{6}{3}=2\\x=-\dfrac{4}{3}\end{matrix}\right.\)

`[x-3]/13+[x-3]/14=[x-3]/15+[x-3]/16`

`=>[x-3]/13+[x-3]/14-[x-3]/15-[x-3]/16=0`

`=>(x-3)(1/13+1/14-1/15-1/16)=0`

  Mà `1/13+1/14-1/15-1/16 \ne 0`

 `=>x-3=0`

 `=>x=3`

Vậy `x=3`

\(\dfrac{x-3}{13}+\dfrac{x-3}{14}=\dfrac{x-3}{15}+\dfrac{x-3}{16}\)

`=> (x-3)/13 + (x-3)/14 - (x-3)/15 - (x-3)/16 =0`

`<=> (x-3)* (1/13 + 1/14 - 1/15 - 1/16) =0`

mà `(1/13 + 1/14 - 1/15 - 1/16)` khác `0`

`=> x-3 =0`

`=> x = 0+3=3`

`(x-3)/13 + (x-3)/14 = (x-3)/15 + (x-3)/16`

`<=> (x-3)/13 - (x-3)/14 - (x-3)/15 - (x-3)/16 = 0`

`=> (1/13 - 1/14 - 1/15 - 1/16).(x-3)=0`

ta thấy : 

`1/13 - 1/14 - 1/15 - 1/16` ko thể `=0`

Nên ta có :

`x-3=0`

`=> x = 0 + 3`

`=> x=3`

\(1+\left(\dfrac{7}{10}+\dfrac{1}{4}\right)\\ =1+\left(\dfrac{14}{20}+\dfrac{5}{20}\right)\\ =1+\left(\dfrac{14+5}{20}\right)\\ =1+\dfrac{19}{20}\\ =\dfrac{20}{20}+\dfrac{19}{20}\\ =\dfrac{20+19}{20}\\ =\dfrac{39}{20}\)